i) Field of the Invention
This invention relates to contaminant detection in paper pulp, and more especially to a method and device for detecting and separating oversize contaminant particles from virgin pulp and recycled pulp. The invention also relates to a method and an apparatus for separating the contaminants from pulp and isolating the oversize contaminants.
ii) Description of the Prior Art
Pressure screens are commonly used in the Pulp and Paper Industry to separate oversize contaminants from good pulp fibre.
A basic industrial pressure screen consists of a housing equipped with a pulp feed port, accept port and reject port. Within the housing, a screen cylinder, also referred to as a screen plate, is designed to allow good fibre to pass through its small apertures but at the same time prevent oversize contaminants from going through. These oversize materials remain on the feed side of the screen cylinder and work their way down its length, until they exit the screen housing through the reject port. Accepted material, material that has passed through the screen cylinder, exits the screen housing via the accept port. Usually a rotor is used to generate pressure pulsations which prevent blinding of the screen plate openings.
Below are some of the more current U.S. patents referencing such screening devices.
1) U.S. Pat. No. 5,624,558 April 1997 “Method and apparatus for screening a fibre suspension” Frank Aaltonen, Frey Frejborg
2) U.S. Pat. No. 5,255,788 October 1993 “Pressure sorter” Reimund Rienecker, Peter Schweiss & Theodor Bahr
3) U.S. Pat. No. 5,232,552 August 1993 “Screening device” N. Jorgen Lundberg, Alf I. Lindstrom
4) U.S. Pat. No. 5,186,332 February 1993 “Paper stock screening apparatus having heavy rejects trap” Derald Hatton, Joseph Constiner & David Suica
Below are a number of “non-typical” screening related patents.
5) U.S. Pat. No. 5,518,584 May 1996 “Device for detecting foreign matter in pulp suspension” Yoshihiko Aikawa
6) Ca 2106211 September 1999 “Method of detecting foreign matter in pulp suspension and device for detecting the same” Yoshihiko Aikawa (same as U.S. Pat. No. 5,518,584 above)
7) U.S. Pat. No. 5,542,542 August 1996 “System for detecting contaminants” John Hoffmann, Robert Gooding, Norman Roberts & Robert Hart (Paprican is the assignee)
8) Ca 2,205,542 May 2002 “System for detecting contaminants” John Hoffmann, Robert Gooding, Norman Roberts & Robert Hart (Paprican is the assignee) (same as U.S. Pat. No. 5,542,542 above)
9) U.S. Pat. No. 4,222,863 September 1980 “Screening apparatus and method” Douglas Young
10) U.S. Pat. No. 5,407,538 April 1995 “Device for separating a mixture of paper pulp and contaminants” Jean Lamort.
A number of patented devices do not use a screening device to separate contaminants. Some patents of interest in this category include:
11) U.S. Pat. No. 4,758,308 July 1988 “System for monitoring contaminants with a detector in a paper pulp stream” Wayne Carr
12) U.S. Pat. No. 5,733,413 March 1998 “Method for removing contaminants from aqueous paper pulp” J. Alan Lawson.